The present invention relates to a lubrication system for engines and more particularly, to a lubrication system capable of carrying out efficient and satisfactory lubrication of the rocker chambers of engines with forced-lubrication systems.
In conventional overhead valve (OHV) engines with splash lubrication systems, for instance as disclosed in Japanese Laid-Open Utility Model Application No. 58-156113, the lubricating oil mist and the blow-by gas in the crank chamber formed in a main engine body casing, are fed into the rocker chambers so that the rocker chambers are lubricated and the blow-by gas separated from the mist of the lubricating oil is supplied to an air cleaner or other system to be burned again.
In general, in the case of forced lubrication system engines such as OHV engines, overhead cam (OHC) engines and the like, the lubricating oil supplied to the rocker chambers returns by its own weight to the crank chamber through oil return passages. In the above mentioned lubrication system, there arises the problem that the rocker chambers are easily filled with the lubricating oil due to blow-back, etc. of the lubricating oil from the oil return passages.
Meanwhile in the case of engines of the type described above, various technical means are employed in order to prevent icing and to accelerate the vaporization of the fuel. For instance, Japanese Laid-Open Utility Model Application No. 56-17713 discloses a technique in which a cooling passage is extended parallel to a suction passage so that the cooling oil flowing through the cooling passage heats the suction passage, thereby accelerating the vaporization of the fuel. Furthermore, Japanese Laid-Open Utility Model Application No. 56-20544 discloses a technique in which an exhaust passage is extended parallel to a suction passage so that the suction passage is heated by the heat of the exhaust gas flowing through the exhaust passage.
However, as the cooling water or exhaust gas must be returned to a cooling water passage or an exhaust pipe, the engine construction becomes complicated. Furthermore a system for heating the suction passage by cooling water cannot be employed in air-cooled engines.